1. Field of the Invention
The present invention relates to an optical element which variably controls the range of exit directions of transmission light, and to a display device, an electronic apparatus, and a lighting device using the same.
2. Description of the Related Art
Display devices such as liquid crystal display devices, for example, are used as information display modules of various kinds of information processing devices such as mobile phones, PDAs (Personal Digital Assistants), ATMs (Automatic Teller Machines), personal computers, and the like.
Further, as the displays are becoming large-scaled and multi-purposed, various luminous intensity distribution characteristics are required for the display devices. Particularly, there are demands for restricting the visible range so that others cannot peep at the display and a demand for not emitting light to undesired directions from the viewpoint of preventing information leakage. For dealing with such demands, an optical film capable of restricting the visible range (or the emission range) of the display device has been proposed and put into practical use. However, in a case where the display device is viewed from a plurality of directions simultaneously, it is necessary to take out the optical element every time. Therefore, there is an increasing demand for acquiring states of a wide visible range and a narrow visible range arbitrarily without going through a trouble of taking out the optical element.
For dealing with such demand, an optical element capable of switching the visible range of the display device between a wide viewing field mode and a narrow viewing field mode has been proposed.
As shown in FIG. 17A and FIG. 17B, this optical element 600 can arbitrarily acquire two states of a wide viewing field mode (see FIG. 17B) that is in an emission state of light 65 and a narrow viewing field mode (see FIG. 17A) by disposing an electrophoretic element 602 between light-transmission regions 601 of high aspect ratio arranged independently on a substrate two-dimensionally and controlling the dispersion state of the electrophoretic element 602 with the electric field generated by the voltage from outside. For example, it is the optical element acquired by: using a transparent substrate; applying, exposing, developing and curing a transparent photosensitive resin layer by applying heat to form the light transmission regions 601; and disposing the electrophoretic element 602 between the light transmission regions 601.
FIG. 18 is a sectional view showing an optical element of a related technique. An optical element 900 includes: a transparent substrate 110; another transparent conductive film 123 formed on the surface of the transparent substrate 110; a plurality of light transmission regions 120 which are formed on the top face of the transparent conductive film 123 by being isolated from each other; electrophoretic elements 140 disposed between those light transmission regions 120; and another transparent substrate 115 which is disposed on the light transmission regions 120 and includes a transparent conductive film 125 on the face that is in contact with the light transmission regions 120. The optical element 900 is disclosed in FIG. 8 of U.S. Pat. No. 7,751,667 B2 (Patent Document 1), for example.
However, there are following issues in the related technique disclosed in FIG. 8 of Patent Document 1.
Since both of the transparent conductive film 123 and the transparent conductive film 125 are disposed in a planar manner in the element regions of the transparent substrate 110 and the transparent substrate 115, transmission of light towards the front face direction is blocked in the region other than the light transmission regions 120 both in the narrow viewing field mode and the wide viewing field mode (see the narrow viewing field mode of FIG. 24A, FIG. 24B and the wide viewing field mode of FIG. 25A, FIG. 25B) and the transmittance in the front face direction is determined according to the pattern size of the light transmission regions. Therefore, it is difficult to improve the transmittance more than that. As a result, the luminance of the liquid crystal display device to which the optical element is mounted is deteriorated.
It is therefore an exemplary object of the present invention to provide an optical element which is capable of increasing the transmittance in the wide viewing field mode than the narrow viewing field mode and capable of suppressing deterioration of the luminance in the wide viewing field mode of the display device to which the optical element is mounted.